After my last track day at Snetterton I headed back to 1320 MINI for a session on the rollers to see if we could get to the bottom of the boost control problems. With a few small changes and the car making healthy power using full boost (slightly over 400hp based on an estimated 15% drive train loss, I only ever compare the outputs at the wheels but folk always seem to want a flywheel figure…), I was all set. I’d also made a few tweaks to the Race Technology dash so I could see when the launch control had been activated.
I think Bedford often gets a bit of a bad rap because the circuit is relatively featureless, lacks any real elevation change and has no motorsport pedigree. Also the noise limits are fairly strict which also doesn’t help but I do like MSVTs approach of noise testing you on the way in it makes life much easier (this time the car recorded an even lower figure than Snetterton). I also think that the lack of solid objects to hit, large run off areas and wide variety of corners make Bedford a good track to really work a car. The GT layout is the longest track in the UK and has a real decent back straight I was looking forward to using the high boost!
Heavy rain over the weekend was still in evidence on Monday with a damp and green track first thing in the morning. Until the damp patches had burnt off the car was pretty lively under heavy acceleration the Quaife diff struggling to find any grip at all. I followed a similar approach to Snetterton and did a few warm up laps on low boost before switching over to high boost. On the first pass down the back straight I saw over 20psi of boost and triggered the check engine light (I’d seen this before and the cause was the MAP sensor hitting 5v). On the second pass down the back straight at over 100mph there was a very loud bang, I braked into the chicane as normal but as soon as I got back on the power it was clear something was very wrong. I glanced down at the dash and could see I had good oil pressure so clearly not a total engine failure, the total lack of power was a massive hint as to where the problem was. I limped back to the pits and popped the bonnet, it didn’t take long to track down the problem! The silicone hose from the turbo to the intercooler had popped off which explained the large bang caused by litres of air under pressure being released. Fortunately it was a quick fix and I was ready to run by the time the car had cooled down. I normally take my laptop with me so I can download data from the ECU or review video footage, sadly this time I’d forgotten the serial to USB converter so I couldn’t reset the check engine light or check the error code. I was fairly confident that the problem was the MAP sensor going out of range and nothing major but decided to run the rest of the day in low boost mode to be on the safe side.
Now some people might think that running about 60% of the maximum boost would be a bit of a let down but I had a great day and really enjoyed driving the car. The car was still more than quick enough and again it was definitely one of the faster track toys on the day.
Another few videos from the track.
A few weeks after Bedford it was back to 1320 MINI to hopefully resolve the boost control issues for good. It was always our intention to have a relatively light spring to control the boost on the road and then use the boost control solenoid for a higher boost level on track. The problem we saw was caused by the wastegate spring being too light, when the demand pressure was reached and the boost control solenoid reduced the duty cycle the gate was being forced wide open and losing several psi of boost pressure; this would then repeat as the boost pressure built again explaining the behaviour I saw at Snetterton. By increasing the wastegate spring pressure the ECU was able to maintain a steady 20psi without upsetting the MAP sensor. It also has the added “bonus” of meaning low boost mode has even more power….
A few flames from the dyno.
Some points to note incase you want to comment… The video is slowed down so sounds nasty and the black smoke is just the uncontrolled ignition of the unburnt fuel caused by the ignition cut, nothing to worry about move along!